The invention relates to a method for producing non-grain-oriented magnetic steel sheet. In this document, xe2x80x9cnon-grain-oriented magnetic steel sheetxe2x80x9d refers to magnetic steel sheet as defined in DIN EN 10106 (xe2x80x9cfinally-annealed magnetic steel sheetxe2x80x9d) and DIN EN 10165 (xe2x80x9cmagnetic sheet which has not been finally-annealedxe2x80x9d). Furthermore, this also includes more strongly anisotropic types, provided they are not deemed to be grain-oriented magnetic steel sheet.
Non-grain-oriented magnetic steel sheets with a thickness ranging from 0.65 to 1 mm are for example used in the production of motors which are only switched on for a short time of operation. Typically, such motors are used in the field of domestic appliances or equipment, or as auxiliary drives in motor vehicles. Such motors are intended to produce high performance, while energy consumption only plays a subordinate role.
A first method for producing non-grain-oriented hot-rolled magnetic steel sheet is known from DE 198 07 122.A1. In the known method, a raw material comprising (in mass per cent) 0.001 to 0.1% C, 0.05 to 3.0% Si, up to 0.85% Al, wherein % Si+2Alxe2x89xa63.0%, and 0.5-2.0% Mn, with the remainder being iron and the usual impurities, is hot rolled, either directly from the casting heat or after reheating, to a temperature of at least 900xc2x0 C. During hot-rolling, two or more forming passes are carried out in a targeted way in the two-phase region austenite/ferrite. In this way, if necessary a cold-rolled and finally-treated magnetic steel sheet can be produced in a manner which saves time and energy, said magnetic steel sheet having improved magnetic characteristics when compared to conventional sheet of this type.
In the conventional production of non-grain-oriented magnetic steel sheet, as is for example described in EP 0 897 993 A1, usually a slab or thin slab cast from a steel of a particular composition, is rough rolled to form a roughed strip. This roughed strip is subsequently hot-rolled in several passes. If required, the hot-rolled strip is annealed and subsequently coiled. After coiling, as a rule, pickling and further annealing of the hot strip take place, said hot strip being finally cold-rolled to final thickness in one step, or in several steps with intermediate annealing. If required, supplementary skin-pass rolling is carried out. If required by the end user, the cold-rolled strip is also subjected to final annealing.
Instead of rough rolling a roughed strip from a cast slab, it is also possible to use thin slabs or to use cast roughed strip directly to produce magnetic sheets. When using cast roughed strip, there is also the option of casting extremely thin strip with dimensions which approximate the dimensions of the hot strip to be produced. Technological advantages and cost advantages can be achieved by integrating casting of such a roughed strip and hot-rolling of such a strip in a continuous process.
Each of the individual processing steps during the production has an influence on the magnetic characteristics of the end product. For this reason for example, the pass sequence and the state of the microstructure in the hot strip during each roll pass are set during hot-rolling, depending on the transformation behaviour of the steel which is governed by the composition of the steel by way of the temperature at the beginning of rolling and the cooling carried out between the individual roll passes, such that the desired magnetic characteristics of the end product are achieved. Likewise, the characteristics of the end product are determined by the annealing temperatures, the coiling temperature and the deformation during cold rolling.
Due to the large number of production steps, the production of magnetic steel sheet is technically demanding and expensive. This is a disadvantage in particular in the case of sheet of increased thickness.
It is thus the object of the invention to provide a method which makes it possible in particular to economically produce thicker magnetic steel sheet which is not grain-oriented and which has good magnetic properties.
This object is met by a method for producing non-grain-oriented hot-rolled magnetic steel sheet in which from a raw material such as cast slabs, strip, roughed strip or thin slabs, said raw material comprising a steel with (in weight per cent)
C: 0.0001-0.05%;
SI: xe2x89xa61.5%;
Al: xe2x89xa60.5%; wherein [%Si]+2[% Al]xe2x89xa61.8;
Mn: 0.1-1.2%;
with the remainder being iron as well as the usual impurities;
is produced; in a finishing roll line at temperatures which are above the Ar1-temperature, a hot strip of a thickness xe2x89xa61.5 mm is rolled, wherein at least the last forming pass of hot rolling is carried out in the mixed region austenite/ferrite, and wherein the total deformation xcex5H achieved during rolling in the mixed region austenite/ferrite is xe2x89xa635%. Optionally, the steel used according to the invention can comprise up to a total of 1.5% of alloying additions, such as P, Sn, Sb, Zr, V, Ti, N, Ni, Co, Nb and/or B.